An exercise apparatus used to simulate skating or roller blading movement in a user includes a pair of sleds or shuttles which include a pedal adapted to support the foot of a user standing thereon. The co-ordinate other than the at least one reference co-ordinate is represented as a combination of an estimate determined from the previous m co-ordinates and a residual error value. The plasma-treated planar textile structures preferably have a high hydrophilic stability when stored in alkaline media. The resulting modified signal is aesthetically pleasing to the user, while indicating to the user that communications with the second party are temporarily interrupted. The folding boat further comprises a safety fence composed along the starboard and port sides.